The invention concerns the detection of faults in sheet and like materials, and has particular, though not exclusive, reference to the detection of faults in tufted fabrics.
In the manufacture of tufted fabrics wherein multiple side-by-side lines of stitches are entered in a backing fabric by respective needles which repeatedly pierce such fabric and co-operate with oscillating loopers disposed at the opposite side of the fabric from the needles to form loops in the backing fabric, any malfunction in the operation of a needle/looper combination or fault in the yarn feed to a needle will manifest itself in a fault in the tufted fabric, which fault, by the nature of the construction of a tufted fabric, will continue along the line of stitching until remedied. Thus, for example, a broken yarn will give rise to a missing line of stitching, whilst a light or loose yarn or a poor knife action will result in some anomaly in the tuft or in the backstitch in the line of stitches in which the non-standard yarn relates.
Present day tufting machines operate at very high speed, and so much so that a fault which remains undetected for only a short time can give rise to an appreciable length of fabric which exhibits the fault. Bearing in mind that tufted fabrics are produced in widths of up to five meters, any appreciable length of faulty fabric which is produced represents a significant financial disadvantage to the producer.